3.2.1. Thermal Expansion

The thermal expansion coefficients (TECs) of fcc-structured (Cr,Al)N and (Al,Cr)N coatings deposited by sputtering were investigated using synchrotron X-ray diffraction at up to 600 ◦C [65]. It was shown that the thermal expansion coefficient increases with an increasing Al content, from about 7 × <sup>10</sup>−6/K at room temperature to 10 × <sup>10</sup>−6/K at 600 ◦C, see Figure 6. Higher mean values of 14.5 × <sup>10</sup>−6/K were reported both for sputtered and arc-deposited (Al70Cr30)N coatings at room temperature [43]. A fair general estimate is thus (10.5 ± 3.5) × <sup>10</sup><sup>−</sup>6/K.

**Figure 5.** Lattice parameter calculated ab initio for CrN, (CrAl)N, (AlCr)N, and AlN coatings and experimentally measured XRD values, redrawn after [63], original © Elsevier.

**Figure 6.** Temperature-dependent thermal expansion coefficients (TECs) of (CrAl)N and (AlCr)N coatings derived from synchrotron experiments, redrawn after [65], original © Elsevier.
